Using new DNA "fingerprinting" techniques, two University of Minnesota researchers have become the first to unequivocally separate hemp plants from marijuana plants with genetic markers. Hemp, a crop grown for durable fiber and nutritious seed, and marijuana, the most abundant illegal drug of abuse in the United States, both belong to the species Cannabis sativa. They differ in levels of the psychoactive drug tetrahydrocannabinol (THC) but are otherwise difficult to tell apart. The technique holds promise for distinguishing different cultivars (domesticated plant lines) in U.S. criminal cases. It may also prove useful in countries where the cultivation of hemp is permitted but marijuana is illegal, as in Canada and Europe. The work appears in the March issue (volume 51, No. 2) of the Journal of Forensic Science.

The new technique is an improvement on previous means of separating the two types of Cannabis, said author George Weiblen, an assistant professor of plant biology in the university's College of Biological Sciences and College of Food, Agricultural and Natural Resource Sciences. For decades it has been possible to identify THC chemically, but the drug is not present in all plant tissues or throughout a plant's life cycle. And other researchers have found that genetic markers known as "short tandem repeats," which are used to identify individuals in paternity and criminal cases, lack the power to distinguish Cannabis cultivars unequivocally.

In tests with three different cultivars of hemp and one of marijuana, the DNA fingerprints of all the cultivars were distinct and nonoverlapping. Weiblen and Shannon L. Datwyler, a postdoctoral associate who is now on the faculty of California State University, Sacramento, found that the AFLP (amplified fragment length polymorphism) technique generated hundreds of genetic markers that together established separate identities for each of the four cultivars.

"We think this technique has the poten
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Contact: Mark Cassutt
cassu003@umn.edu
612-624-8038
University of Minnesota
22-Mar-2006

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